Valve released its acclaimed first person puzzle shooter Portal 2 back in April and since then players have been waiting for Valve to fulfill its promise and release some downloadable content for the game. Today Valve said that the first DLC pack for the game, titled Peer Review, will be released for free for the PC, Mac, Xbox 360 and PS3 versions. PC and Mac owners will get the DLC pack via an automatic update to Portal 2 on Steam.

Peer Review will feature a continuation of the game's co-op campaign as you and a buddy will once again take on the roles of of the somewhat goofy robots P-Body and Atlas. They will be going through a new test track in Aperture Science and both will have to deal once again with the evil AI GLaDOS. In addition, Peer Review will also add a new Challenge Mode for both the single and co-op campaigns, although details about what that mode will be like have yet to be revealed. Finally the DLC adds new leaderboards for the new Challenge Mode so you can compare your scores with other Portal 2 players.

In addition to today's DLC announcement, Valve revealed that the third and final part of the official Portal 2 soundtrack is now available for download at the game's web site. Players can now get all 64 separate tracks from the game's soundtrack for free. In addition, a number of the game's music tracks can also be downloaded for use as ringtones for iPhones and Android-based devices.